IV.R397 — 0vbb Prediction: must exist; rate proportional to ||^2

Neutrinoless double beta decay (A,Z)->(A,Z+2)+2e^- must exist: neutrinos are Majorana (IV.T146), L is not conserved. Rate Gamma(0vbb) proportional to G_beta * |M_nucl|^2 * ||^2 where =|sum_i U_ei^2*m_i| (Majorana effective mass). Predicted central value (naive PMNS from sigma-matrix): ~ 19 meV, range [9,31] meV. Consistent with KamLAND-Zen (<36-156 meV). Within LEGEND-1000 reach (~10 meV sensitivity). Nuclear matrix element M_nucl not derived in tau-framework (conjectural). Scope conjectural for quantitative rate; structural prediction that 0vbb exists is tau-effective.